Electrodeposition of lead



Patented Feb. 4, 1947 ELECTRODEPO SITION OF LEAD Allen G. Gray, RockyRiver, Ohio, assignor to E. I. du Pont de Nemours & Company, Wilmington,Del., a corporation of Delaware No Drawing. Application September 22,1942, Serial No. 459,282

11 Claims. 1

This invention relates to electrodeposition and more particularly toimproved compositions and processes for electrodepositing lead. Ideally,the invention consists in dry, free-flowing lead sulfamate platingcompositions which preferably contain an anthraquinone sulfonate, and inlead plating processes wherein such compositions are employed.

Systems for electrodepositing lead have heretofore been restricted intheir usefulness through their lack of ability to produce a good initialdeposit in low current density areas upon the cathode. This inabihty,commonly referred to as lack of covering power, is especially pronouncedwhen the cathode is such a metal as cast iron or malleable iron orcertain alloy steels. Failure to secure adequate coverage is aparticularly serious objection when the cathode is being lead plated toprotect it against corrosion.

It is an object of the present invention to pro- H vide improvedcompositions and processes for the electrodeposition of lead over a widerange of current densities and particularly having good covering powerat low current densities. A further object is to provide compositionsand processes for the production of dense, adherent, nonporous, andductile electrodeposits of lead. A further object is to provide leadplating compositions which are dry, free-flowing; and readily soluble inwater, and which are particularly adapted to the preparation of novelplating baths having improved covering power in low current densityranges. Further objects will appear hereinafter. e

Theforegoing and other objects of thisinvention are accomplished byprocesses in which lead is electrodeposited in the presence of ananthraquinone sulfonate, and are further accomplished by dryelectrodepositing compositions and by electrodepositing solutions inwhich an anthraquinone sulfonate is present. The objects areaccomplished with especial success by lead sulfamate electroplatingsolutions in which an anthraquinone sulfonate is present, and by drysolid products comprising dry reaction mixtures of litharge and sulfamicacid suitable for dissolution in waterto' give such electroplatingbaths. The processes and compositions of this invention arecharacterized by their ability to efiect deposition of lead at lowcurrent densities. The benefits of the invention are obtained with leadplating baths over a wide pH range, but are especially apparent in acidplating systems; that is, in electroplating compositions and bathshaving a pH lower than about 7, and especially below about 4.2. In suchacid systems the difficulty of getting adequate coverage at low currentdensities is more pronounced than in alkaline baths and the benefits tobe derived from the inclusionof anfanthraquinone sulfonate are enhanced.

According to this invention any anthraquinone sulionate may be employedin an electrouepositmg composition. there may be used, lot instance,monosulionic acids such as l-anthraqul none sulionlc acid orz-antnraqumohe suiionic acid or polysuliohic acids such as is-anthraquinone disuliomc acid or 2,l -anthraqumone disuiionic acid. Thebath-soluble salts or the suli'onic acids such as the sodium, potassium,or ammonium salts or partial salts, may suitably be used, and because oftheir excellent solubility, ease of preparation, and ease or handling indry form, the sodium salts of the sulionlc acids may be preferred. Themanner or adding the suli'onic acid is comparatively unimportant sincewhether the addition agent s present as an acid or as a salt or as apartial salt will depend upon the pH of the bath. For purposes 01' thisdescription where reference is made to a suli'onate, it will beunderstood that this may be a salt or partial salt or the free acid.

The amount of an antnraquinone sulfonate to include in an electroplatingcomposition or bath will vary depending upon the plating system involved, the metal being plated, the magnitude of eiiect desired, andother similar factors. The amount can best be determined by a few simpletests in the particular bath to be used. In general it will be foundthat from about .05 to 5.0 grams per liter of anthraquinone sulfonatewill be satisfactory.

Anthraquinone sulfonates may be used in electroplating baths incombination with other addition agents. By far the best results areobtained by the use of a sulfite cellulose waste which coacts with theanthraquinone sulfonate to produce excellent results. Sulfite cellulosewaste is a well known commodity of commerce and it has previously beenfound useful in certain plating systems as an addition agent in its ownright. Lignin sulfonic acid derlve'd from sulfite cellulose waste, maybe used instead with substantially equivalent results. This and otherderivatives of a similar nature are known to be equivalent to sulfitecellulose waste and they require no extended discussion.

When a second addition agent is used in combination with theanthraquinone sulfonate the amount of the second addition may also becon-' siderably varied. For instance, when the second agent is sulfitecellulose waste, the amount used may vary from about .25 to 15 grams perliter and more preferably from about 1 to 5 grams per liter.

When reference is made herein to electrodeposition of lead it will beunderstood that the lead may be co-deposited with another metal ormetals to produce alloys. The invention is applicable, for instance, inthe co-electrodeposition of lead and antimony.

Benefits are obtained by usin-g'an anthraquinone sulionate in anylea-delectrodepositing bath according to the present invention. Asalready noted above the improvement is particularly api parent in acidplating systems, but neutral or alkaline baths may also be modified toadvantage. Typical of lead-plating baths which may be modified by theinclusion of an anthraquinone sulfonate are the fiuoborate, sulfamate,and fluosilicate baths described in the following examples. forinstance, the acetate bath (Metal Finishing 38, 533 (1940)) containing10 gm.

Pb ((3211302) 2.3H2O

12 to 16 gm. Na(CzI-Is02) 2 gm. acetic acid, .4 to .6 gm. glue, and 3 to4 drops cresolper 100 ml. solution; the perchlorate bath (Trans. Am.

Electrochem, Soc. 23, 159 (1913)) containing 5% lead, 2 to 5%. freeperchloric acid, and .05 peptone; and baths havin as a principalelectrolyte lead nitrate, lead oxalate, lead dithionate. lead cyanide,or sodium plumbite.

The invention Will be better understood by reference to the followingillustrative examples:

Example I A lead fiuoborate electroplating bath was prepared asdescribed in the Transactions of the Electrochemical Society, vol. 36,page 243, having the following composition:

v Grams/liter Hydrofluoric acid (50% solution) 160 Boric acid 74.4 Basiclead carbonate 129 Glue 0.1

.To this aqueous solution there was added 0.2

gram/liter of l-anthraquinone sodium sulfonate to obtain a bath of thisinvention.

Copper test plates were electroplated in this solution at variouscurrent densities. 'It wasv found that complete coveragev of the. testplate withleadwas effected inoneminute at all cur Example II A leadplating solution was made up having the following composition:

Grams/liter Litharge 150 Sulfamic acid e 1'50 Ammonium sulfamate 75l-anthraquinone sodium sulfonate 0.5

Sulfite cellulose waste 5 The solution had a pH of 1.5.

Copper test plates were lead plated in this solution at various currentdensities. A smooth,- dense, lustrous deposit was secured in one. minuteat current densities as low as 0.9 amp/sq. ft. Test plates which wereelectroplated with lead in a solution. having similar compositions,

except thatithe l-anthraquinone sodium sulfonate was omitted, gave nocoverage in. one min:

, ute at current densities below 5 amp/sq. ft.

Example III-- A bath wasmade up having the same'c'oinpe- Other bathswhich may be modified are sition as in Example II above,-except thatinstead of l-anthraquinone sodium sulfonate, there was used as theaddition agent 1,8-anthraquinone sodium disulfonate. The test platesshowed that without the anthraquinone disulionate, cover-' age wasincomplete in one minute at current densities below 5 amp/sq. ft.Whereas with the anthraquinone disulfonate, coverage was complete atcurrent densities as low as 2 amp/sq. ft.

It will be seen from the above examples that a substantial improvementin covering power cl certain lead electroplating baths is effected bythe inclusion therein of an anthraquinone sulfonate. This improvement isnoted also in other lead electroplating baths, such as the fluosilicateor acetate baths. A typical lead fluosilicate bath in which improvementis effected is shown in Plating and Finishing Guidebook (1941) p. 48,bath No. II, having the composition:

Grams/liter Lead fiuosilica 150 Free fluosilicic acid 30 Glue 3 as isevidenced'by a change in color of the mixture from that of the lithargeto substantially white. A'plating composition of superior properties isobtained as a dry, very readily water 501- uble, free-flowing product.

The proportions of litharge and sulfamic acid used in making the dryreaction product should be about those required to give a bath of thede-.

sired characteristics when the product is dissolved in water at aconcentration such as indicated in Example 11 above. Thus, the proportions should be such as to give a pH of less than 7 and preferably, lessthan 4.2. The amount of ammonium sulfamate should be appreciable, butnot the major proportion of the product, comprising about from 5 to 30%of the mixture. A preferred mixture might contain, for instance, thereacted equivalent of about 40 parts of litharge, 40 parts of sulfamicacid and 20 parts of ammonium sulfamate, but it will be understood thatthese proportions are susceptible to considerable variation.

By including an anthraquinone sulfonate and, optionally, anotheraddition agent such as sulfite cellulose waste, in a dry lead sulfamateor litharge-sulfamic acid reaction product, there is obtained acomplete, balanced product which is ideally suited for use by the trade.Such a proddot, for instance, may readily be dissolved in water to givelead plating solutions of this invention without the inconvenience ofmeasuring out or weighing the separate constituents.

By dissolving a suitable sulfamate-lead composition, such as forinstance one of the abovedescribed compositions in a proper amount oiwater, there may be produced a lead sulfamate plating bath which isparticularly amenable'to the action of an anthraquinohe sulfbnateir'fac'cordance with this invention. Such a solution will generally containfrom about 50 to 400 grams/liter of dissolved lead (expressed as Pb) andpreferably from about 100 to 200 grams/liter. The total sulfamatecontent will usually be equivalent to from about 50 to 450 grams/literof sulfamic acid and preferably from about 100 to 250 grams/liter.

The weight ratio of combined lead content, expressed as Pb, to leadsuli'amate plus free suli'amio acid content is important. The Weightratio of combined Pb to (NI-12SOzPb+NI-IzSOsH) should be from about 1:1to 1:3 and preferably about 1:2. The amount of free sulfamic acidpresent in the bath should be from about to grams/liter. It will beunderstood that there will preferably be present suliamate incombination as ammonium suif'amate and that this sulfamate is inaddition to the lead sulfamate and sulf'amic acid. The ammoniumsuliamate content preferably will be from about 25 to 100 grams/liter.

Lead sulfamate plating baths in which anthraquinone sulfonates areparticularly effective are definitely acidic. The pH should ordinarilybe from about 0.1 to about 4.2 and preferably should be from 1.0 to 3.0.Particularly excellent results have been obtained using a pH of about1.3 to 2.0. If in making up the bath sulfamic acid is used as such, thepH may be adjusted by appropriate additions of sulfamic acid. If part orall of the sulfamic acid is added to the bath in the form of a salt,then the pH may be adjusted by the use of another acid such as formicacid, acetic acid, or nitric acid.

In the operation of the lead sulfamate bath lead anodes are used toreplenish the lead content of the solution and maintain the compositionas above indicated, but in some instances it may be found convenient toadjust the composition of the bath by appropriate additions of basiclead compositions such as litharge and by the addition of sulfamic acid.

While certain illustrative compositions and processes have been shown,it will be understood that the invention is not limited thereby but thatone skilled in the art, without departing from the spirit of theinvention, may readily devise numerous composition and processes for theelectrodeposition of lead.

I claim:

1. In a process for the electrodeposition of lead, the step comprisingefiecting electrodeposition of lead from an acidic, aqueous leadelectrodepositing solution in the presence of about from .05 to 5.0grams per liter of an anthraquinone sulfohate and 1.0 to 5.0 grams perliter of sulfite cellulose Waste.

2. In a process for the electrodeposition of lead, the step comprisingeifecting electrodeposition of lead from an aqueous solution containingabout from to 400 grams per liter of lead, 50 to 450 grams per liter ofsulfamic acid, .05 to 5.0 grams per liter of an anthraquinone sulfonate,and from 1.0 to 5.0 grams per liter of sulfite cellulose waste.

3. A lead electrodepositing composition in dry form, comprising a leadcompound and an anthraquinone sulfonate, the proportions ofanthraquinone sulfonate and other constituents being such that when thecomposition is dissolved in water to make a solution of suitableconcentration for electroplating, the anthraquinone is present in thesolution at a concentration of from .05 to 5.0 grams per liter.

4. A lead electrodepositing" composition in dry form, comprising a leadsulfamate and an anthraquinone sulfonate, the proportions ofanthraquinone sulfonate and other constituents being such that when thecomposition is dissolved in water to make a solution of suitableconcentration for electroplating, the anthraquinone is present in thesolution at a concentration of from .05 to 5.0 grams per liter.

5. A lead electrodepositing composition in dry form comprising litharge,sulfamic acid, and an anthraquinone sulfonate, the proportions ofanthraquinone sulfonate and other constituents being such that when thecomposition is dissolved in water to make a solution of suitableconcentration for electroplating, the anthraquinone is present in thesolution at a concentration of from .05 to 5.0 grams per liter.

6. A lead electrodepositing composition in dry form comprising litharge,sulfamic acid, an anthraquinone sulfonate, and sulfite cellulose waste,the proportions of anthraquinone sulfonate and other constituents beingsuch that when the composition is dissolved in water to make a solutionof suitable concentration for electroplating, the anthraquinone ispresent in the solution at a concentration of from .05 to 5.0 grams perliter,

7. An aqueous lead sulfamate plating solution comprising ananthraquinone sulfonate, in a concentration of about from 0.5 to 5.0grams per liter ammonium sulfamate, and the reaction product of suchproportions of litharge and sulfamic acid as to give a pH of from about0.1 to 4.2 in the bath.

8. An aqueous lead sulfamate plating solution comprising l-anthraquinonesodium sulfonate in a concentration of about from .05 to 5.0 grams perliter and the reaction product of about 40 parts by weight of litharge,40 parts of sulfamic acid, and 20 parts of ammonium sulfamate.

9. In a process for the electrodeposition of lead, the step comprisingeiiecting electrodeposition of lead from an aqueous leadelectrodepositing solution in the presence of about from 0.05 to 5.0grams per liter of an anthraquinone sulfonate.

10. In a process for the electrodeposition of lead, the step comprisingeffecting electrodeposition of lead from an aqueous lead sulfamateelectrodepositing solution in the presence of about from 0.05 to 5.0grams per liter of an anthraquinone sulphonate.

11. In a process for the electrodeposition of lead, the step comprisingeffecting electrodeposition of lead from an aqueous lead fiuoborateelectrodepositing solution in the presence of about from 0.05 to 5.0grams per liter of an anthraquinone sulfonate.

ALLEN G. GRAY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,271,209 Schlotter Jan. 27, 19422,294,053 Stack, et a1 Aug. 25, 1942 1,515,042 Heck Nov. 11, 19242,318,592 Cupery May 11, 1943 OTHER REFERENCES Trans. Electrochem.Society, vol. '76 (1939) page 371, copy in Div. 56.

